What is the crevice volume?
CREVICE VOLUME IS THE VOLUME BETWEEN THE PISTON AND THE CYLINDER LINER. THE EFFECT OF THIS VOLUME IS VERY APPRECIABLE ON THE ENGINE PERFORMANCE.
Are narrow regions in the combustion chamber into which the flame Cannot propagate because it is smaller than the quenching distance?
Crevices – these are narrow regions in the combustion chamber into which the flame cannot propagate because it is smaller than the quenching distance. Crevices are located around the piston, head gasket, spark plug and valve seats and represent about 1 to 2% of the clearance volume.
What is mean by crevices inside of combustion chamber?
Crevices—narrow volumes present around the surface of the combustion chamber—are regions of high enough surface-to-volume ratio to prevent flame propagation.
What is the effect of humidity on knocking?
Clearly, an increase in the water content in air substantially increases the Knock Limited Spark Timing (KLST), as is known in practice. From this we conclude that the presence of water vapor increases the resistance to knocking of the gaseous fuel/air mixture substantially.
What is the effect of humidity on knocking Mcq?
Explanation: Increasing the humidity of the entering air tends to reduce knocking by reducing the reaction time.
Where do crevices occur in an engine?
Crevices are present between the piston head and liner, along gasket joints between the engine head and block, along the seats of the intake and exhaust valves, and between the spark plug threads. During compression and combustion, these volumes are filled with unburned charge.
What is knocking in an engine?
knocking, in an internal-combustion engine, sharp sounds caused by premature combustion of part of the compressed air-fuel mixture in the cylinder. In a properly functioning engine, the charge burns with the flame front progressing smoothly from the point of ignition across the combustion chamber.
What is flame front propagation?
Flame propagation is defined as the progress (spread) of the flame inside the engine cylinder (combustible environment) outward from the point at which the combustion started. Flame generally propagates spherically. The rate of radial propagation of flame is known as flame speed. It is typically measured in m/s.
How is the knocking tendency increased?
In CI engine, the knocking tendency increases with a decrease in compression ratio. If the compression ratio is low in CI engine, there will not be enough temperature generation for ignition of the fuel-air mixture. So fuel will get accumulated in the chamber.
What causes detonation?
Detonation occurs when excessive heat and pressure in the combustion chamber causes the air/fuel mixture to ignite on its own. Instead of a typical single flame kernel within the chamber, this creates multiple flames which collide with explosive force.
What is the difference between knocking and detonation?
In general, detonation is the cause and knocking is the after effect. Those who deal the terms knocking and detonation as a separate phenomenon, do so by referring auto-ignition theory as knocking and detonation theory as detonation. So, depending on the context it can mean the same thing or different thing.
What is knocking in SI and CI engine?
In an SI engine, knocking occurs after the mixture is ignited by the spark plug. In a CI engine, knocking occurs at starting of the combustion process. 2] Knocking causes due to low ignition lag. Knocking causes due to the high ignition lag.
What is ignition lag in SI engine?
Ignition lag is the time interval in the process of chemical reaction during which. molecules get heated up to self ignition temperature , get ignited and produce a self. propagating nucleus of flame. The ignition lag is generally expressed in terms of crank.
What is scavenging air?
Scavenging is the process of replacing the exhaust gas in a cylinder of an internal combustion engine with the fresh air/fuel mixture (or fresh air, in the case of direct-injection engines) for the next cycle.
How knocking can be reduced?
In spark ignition (SI) engines, the possibility of knocking can be reduced by decreasing compression ratio as a reduction in compression ratio will result in the generation of lower peak temperature. In SI engine, knocking occurs before TDC and because of early combustion of charge/more than one flame propagation.
What is SI and CI engine?
Definition of Si engine and Ci engine Si engine is internal combustion engine that operates on the principle of spark ignition. It uses petrol and utilizes the Otto cycle. The diesel (Ci) engine is also an internal combustion engine, which uses diesel fuel and operates on diesel cycle.
What is octane and cetane number?
The higher the number, the better the fuel burns within the engine of a vehicle. The cetane number is similar to the octane rating in that it is a rating assigned to a fuel to rate the quality of its combustion. The difference is that octane rating rates gasoline whereas cetane rates diesel.